也许外星人就在我们身边，只是我们看不到而已

What if alien spacecraft are already in our midst – and we don't know about them because they're tiny nano-structures? That's the new idea put forward by one scientist seeking to explain the Fermi paradox.

如果外星人的太空船已经来到我们人类中间，而我们却不知道它们，因为它们是微小的纳米结构呢?这是一位试图解释费米悖论的科学家提出的新观点。

This paradox – named after Italian-American physicist Enrico Fermi – posits that because the Milky Way is so vast and so old, the chances of alien civilisations being out there is actually pretty high... so where are they?

这一悖论——以意大利裔美国物理学家恩里科·费米的名字命名——提出了这样一个假设:由于银河系如此浩瀚而古老，外星文明存在的几率实际上相当高……那么他们在哪里呢?

Maybe they're buzzing around the Universe in micro-machines just a nanometre long, suggests astrophysicist Zaza Osmanov from the Free University of Tbilisi in Georgia. What's more, he's provided some pretty detailed calculations to go along with this slightly whacky-sounding idea.

来自格鲁吉亚第比利斯自由大学的天体物理学家扎扎·奥斯马诺夫认为，也许它们是在一纳米长的微型机器里绕着宇宙飞行。更重要的是，他提供了一些非常详细的计算，以配合这个听起来有点古怪的想法。

Now it's worth mentioning that Osmanov's paper has yet to be peer-reviewed, so we can't place too much importance on it just yet – but it does open up an intriguing possibility about how other civilisations might one day reach us.

现在值得一提的是，奥斯马诺夫的论文还没有经过同行评议，所以我们目前还不能把它放在太重要的位置——但它确实为我们提供了一个有趣的可能性，即有一天其他文明可能会如何影响我们。

The new study is based on the established idea of von Neumann probes: the thinking goes that aliens could send out self-replicating spacecraft to explore the galaxies, without having to risk leaving their home planet themselves.

这项新研究基于冯·诺依曼探测器的既定理念:外星人可以发射自我复制的宇宙飞船去探索星系，而不必冒险离开自己的星球。

Previous attempts to figure out how von Neumann probes could function have hit a common problem – self-replication needs a steady supply of new materials, and it's not clear if deep space has enough suitable planets or rocky bodies to go around.

先前试图找出冯·诺依曼探测器如何工作的尝试遇到了一个共同的问题——自我复制需要稳定的新材料供应，目前还不清楚深空是否有足够合适的行星或岩石体环绕。

To get around the issue, Osmanov has shrunk the scale right down. Microscopic probes would need much less in the way of materials, and could rely on hydrogen atoms floating through the interstellar dust for power.

为了解决这个问题，奥斯曼诺夫将规模定位微型。微型探测器在材料方面的需求要少得多，而且可以依靠漂浮在星际尘埃中的氢原子来获取能量。

These nanoscale probes would, in theory, be much more efficient than any previously imagined, and could replicate in just a few years – getting around the Universe relatively quickly. They'd also become very numerous (up to the level of trillions of billions) in a few short light-years of steady reproduction.

从理论上讲，这些纳米级的探测器比之前想象的要高效得多，而且可以在短短几年内进行复制——以相对较快的速度环绕宇宙。它们也会在几光年的稳定繁殖中变得非常多(达到几万亿级)。